Method of producing aluminum base alloys



Patented May 29, 1945 Philip '1. Stroup, New Remington, r... mm.-

toAl um Company of America, Pittsburgh,

Pa., a corporation of Pennsylvania No Drawing. Application August 14, 1940, Serial No. 352,525

7 Claims. ('01, 75-138) This invention relates to aluminum base alloys containing magnesium and more particularly it is concerned with such alloys having beryllium'as an alloying constituent.

Alloys of aluminum containing magnesium and beryllium as alloying elements are well known. For example, in my copending applications Serial Nos. 295,642 and 295,644, filed September 19, 1939, I have described an aluminum base alloy containing magnesium to which very small amounts oi beryllium or of beryllium and lithium are added to prevent oxidation and loss of magnesium content from the alloy while it is in a molten condition.

However, it has heretofore been quite difllcult to introduce even very small amounts of beryllium into aluminum base alloys. If metallic beryllium is charged into the molten base metal, it does not alloy readily with the base metal. Moreover, extremely high temperatures must be employed, and at such temperatures loss from the melt due to oxidation constitutes a serious problem. In addition, metallic beryllium is relatively expensive. In order to reduce the cost of forming such alloys, various beryllium compounds, such as the fluorides, have been used which decompose in the molten metal and alloy their beryllium component with the base metal, but such compounds, upon decomposition, introduce but very little beryllium into the molten metal and their use is unsatisfactory.

The object or this invention, accordingly, is to provide a relatively inexpensive and yet effective method for introducing beryllium into alloys of aluminum containing magnesium. More particularly, the object of the invention is to devise a method whereby beryllium may be alloyed with such alloys by decomposition of a compound of beryllium in the molten metal. A specific object is to provide a commercially practical and economical way for introducing beryllium as an alloying constituent into aluminum-magnesium alloys by which method lithium also is introduced into such alloys. Other objects will appear in the following description of the invention.

I have found that, while only very small amounts of beryllium can be introduced into a molten aluminum base alloy containing 0.5 per cent or more of magnesium by decomposition of beryllium fluoride or other compounds of beryllium in the molten alloy, much greater amounts of beryllium can be introduced into the molten metal as an alloying constituent if a mixture of beryllium fluoride with lithium fluoride be added to the melt. The presence of the admixed lithium 5 fluoride appears to aflect the behavior or the beryllium fluoride as it decomposes in the alloy, resulting not only in a much greater yield of beryllium than is effected by the decomposition of beryllium fluoride alone but also causing the beryllium liberated from its compound to alloy more readily with the base metal. The alloy which is produced in this way, in addition to containing magnesium and beryllium, also has a small lithium content which generally is beneficial in the alloy since lithium, like beryllium, prevents oxidation of the magnesium constituent and imparts desirable properties to thealloy. While beryllium and lithium may be added in this manner to any aluminum base alloy containing more than about 0.5 per cent of magnesium, I prefer to maintain the magnesium content below about 15 per cent, which represents the limit of magnesium content in useful, commercial aluminum base alloys.

In actual tests to demonstrate the operation of my invention, 5 grams of beryllium fluoride were charged into 500 grams of an aluminum base alloy containing 8 per cent of magnesium. After the decomposition of the beryllium fluoride, the alloy was found to have a beryllium content of but 0.004 per cent. However, when various amounts between 5 and 20 grams of lithium fluoride were admixed and charged with the 5 grams of beryllium fluoride into the same amount of the same alloy, the beryllium content increased accordingly to between 0.05 per cent and 0.09 per cent. This may be summarized as follows:

Chemical analysis Amounatfigydded to of Buoy after treatment LiF BBF: Li Be Grams Gm ms Per cent .Per cent 5 0.004

Greater amounts of lithium fluoride in propor eutectic seems to form when about 4 parts of lithium fluoride are admixed with 1 part of beryllium fluoride and this molten eutectic mixture iavors reaction at normal melting temperatures 01' aluminum-magnesium alloys.

I claim: I

1. The method of alloying beryllium into an aluminum base alloy containing magnesium to provide an increased yield of beryllium, which method consists in adding a mixture of beryllium fluoride and at least an equal part lithium fluoride to the alloy while said alloy is in the molten state. I

2. The method of alloying'beryllium into an aluminum base alloy containing magnesium to provide an increased yield 01 beryllium, which method consists in adding a mixture of 1 part beryllium fluoride and between about 1 part and about 4 parts lithium fluoride to the alloy while said alloy is in the molten state.

3. The method of alloying beryllium into an aluminum base alloy containing between about 0.5 per cent and about 15 per cent of magnesium to provide an increased yield of beryllium which method consists in adding a mixture of beryllium fluoride and at least an equal part lithium fluoride to the alloy while said alloy is in the molten state.

4. The method 01 alloying beryllium with an aluminum base alloy containing between about 0.5 per cent and about 15 per cent oi! magnesium to provide an increased yield of beryllium, which method consists in adding a mixture of 1 part beryllium fluoride and between about, 1 part andabout 4 parts lithium fluoride to the alloy while said alloy is in the molten state.

5. In the process of alloying beryllium with an aluminum base alloy containing magnesium by decomposing beryllium fluoride in contact with the molten alloy, the method of increasing the yield of beryllium from said beryllium fluoride decomposed in contact with the alloy which comprises the step of admixing in contact with said molten alloy beryllium fluoride and at least an equal part lithium fluoride.

6. In the process of alloying beryllium with an aluminum base alloy containing magnesium by decomposing beryllium fluoride in contact with the molten alloy, the method of increasing the yield of beryllium from said beryllium fluoride which comprises the step of admixing in contact with said molten alloy between about 1 part and about 4 parts lithium fluoride and 1 part of beryllium fluoride.

7. In the process of alloying beryllium with an aluminum base alloy containing between about 0.5 per cent and about 15 per cent of magnesium by decomposing beryllium fluoride in contact with the molten alloy, the method of increasing the yield of beryllium from said beryllium fluoride which comprises the step of admixing in contact with said molten alloy between about 1 part and about 4 parts of lithium fluoride and 1 part of beryllium fluoride.

PHILIP T. STROUP. 

